The field of the invention relates to controlling the wheel slip of a driven wheel coupled to an internal combustion engine.
When a vehicle (such as an automobile, truck or motorcycle) accelerates over a slippery surface, the engine torque applied to the driven wheel may cause abrupt acceleration or wheel spin. A temporary loss in vehicle control may result. An approach towards solving the problem of wheel slip is disclosed in German patents 2058819 and 2832739 wherein the engine throttle is controlled in inverse relation to a measured difference in rotation between a driven wheel and a nondriven wheel. U.S. Pat. No. 4,554,990 issued to Kamiya et al. discloses a control system wherein the difference in rotation between a driven wheel and a nondriven wheel is used as a feedback variable.
The inventors herein have recognized numerous disadvantages of these prior approaches. One disadvantage is that torque is removed from the drive wheel by controlling an engine input (throttle). Thus, torque is not removed from the drive wheel until after a time delay through the engine is incurred. Another disadvantage is that the feedback variables for engine torque output are derived from delayed variables such as engine speed and wheel speed. These feedback variables are therefore delayed by a time delay through the engine and drivetrain resulting in a feedback loop with poor transient response time and stability.
An approach to wheel slip control for double axle vehicles is disclosed in French patent reference FR 2590-525 issued to Rena. More specifically, in response to a detection of wheel slip in one of the double axles, the wheel of the adjacent axle is hydraulically raised thereby increasing the load on the other axle. A disadvantage of this approach is that the net force against all the wheels remains the same regardless of suspension control. Thus, cornering forces on the wheels are not improved and loss of vehicular control may ensue. Another disadvantage is that the slip control is limited only to the double axles rather than the entire vehicle, therefore, the disclosed slip control does not appear to be applicable to automobiles. Still another disadvantage of this approach is that the engine continues to apply torque to the slipping wheel. The inventor herein contends that there is no teaching or suggestion of coordinated engine/suspension control. The inventor further contends that the disclosure of the Rena patent addresses the problem of traction control rather than vehicular control while accelerating over slippery surfaces.